The mammalian neocortex is the product of a complex evolutionary history. Research on the organization of sensory projections to the telencephalon of nonmammalian vertebrates has demonstrated the presence of cortical equivalent "cluster" of neurons within the Dorsal Ventricular Ridge (DVR) of the telencephalon. These "clonal clusters" may correspond to individual laminae of the mammalian neocortex. The microcircuitry of connections between "clusters" within the tectofugal pathways appears to correspond to the interlaminar organization of extrastriate visual pathways of the neocortex. Further analysis of this pathway will help clarify the role of the extrastriate system in visual performance. Studies will concentrate on the organization of visual pathways within the DVR, the relationship of the DVR to the neocortex, and possible role of the subventricular zone of Stensaas in the ontogeny of neocortex in mammals. The DVR may correspond to the Subventricular Zone (SVZ) of Stensaas in the developing neocortex of mammals. Specific studies will include: A. Analysis of the organization, histochemistry and morphology of the neurons of the tectofugal pathway in the DVR of birds. B. Interrelationship of the thalamofugal and tectofugal pathways. C. Production of monoclonal antibodies to identify "clonal clusters" and their possible cross reactivity with single laminae of the neocortex of mammals. E. Investigate the role of the SVZ of mammals as a possible representative of the Dorsal Ventricular Ridge, and its participation in the development of neocortex. These studies will clarify our understanding of the role of tectofugal pathways in vision, the evolutionary origins of the mammalian neocortex, and both normal and abnormal developmental events in the ontogeny of the mammalian neocortex. Methods to be employed include pathway tracing methods, single cell filling, immunohistochemistry, monoclonal antibodies and in situ hybridization to identify the transmitters/peptides, receptors and related proteins mediating organization and communication in these two pathways.